1. Field of the Invention
The present invention relates to a raw material for powder metallurgy and a manufacturing method thereof. More specifically, the present invention relates to a highly reliable raw material for an alumina particle dispersed aluminum matrix composite and a manufacturing method thereof.
2. Description of the Background Art
Though various and many alumina particle dispersed aluminum matrix composite materials and raw materials therefor have been developed, almost none has been successively used in practice, because of inadequate reliability. Durability, flaw ratio and cost are major problems to be solved. What is important in solving these problems is how to mix alumina powder and aluminum alloy powder finely and uniformly. Most of the conventional approaches simply reduce the particle size (or mean particle diameter) of the powder.
The smaller the particle size of the powder, the higher the cost, and when the particle size is simply reduced, there arises a new problem of agglomeration. The agglomerated powder is the main cause of degraded reliability. Once generated, agglomerated powder cannot be readily separated, and the agglomerated powder is kept agglomerated until in the final product. The size of the agglomeration may attain as large as 100 .mu.m to several mm, and therefore generation of the agglomerated powder causes the same defect as a foreign matter mixed in the final product. It decreases strength, fatigue strength, impact strength, toughness and heat resistance, and significantly degrades reliability of the material.
Conventionally, most of the materials are prepared by simply mixing alumina powder just commercially available, with aluminum alloy powder by means of a V-blender. Even when some particle size adjustment is performed, the adjustment may be simple screening out of bulky particles by sieve classification.